PROPERTIES  OF  SOME  PHOSPHATE 
CEMENTS 


JOHN  RUSSELL  GREEN 
THESIS 

FOR  THE 

DEGREE  OF  BACHELOR  OF  SCIENCE 

IN 

CERAMIC  ENGINEERING 


COLLEGE  OF  ENGINEERING 
UNIVERSITY  OF  ILLINOIS 


1922 


Digitized  by  the  Internet  Archive 
in  2016 


https://archive.org/details/propertiesofsomeOOgree 


■ 


PROPERTIES  OF  SOME  PHOSPHATE  CEMENTS 
CONTENTS 

Page 

I.  Introduction  1 

II.  Scope  and  Results  of  Former  Work  .....  1-2 

III.  Basis  of  Study 2-4 

IV.  Preliminary  Study 4-13 

A.  Objects  ........  4 

B.  Selection  for  Study  .............  5 

C.  Preparation  of  Powders 6-S 

D.  Results  ...  .........  9-12 

E.  Conclusions . 12-14 

V.  Final  Study  14-22 

A.  Objects 14 

B.  Preparation  of  Powders  ...........  14-17 

C.  Results  ...................  17-21 

D.  Conclusions 21-22 

VI,  Summary 22-23 


PROPERTIES  OF  SOME  PHOSPHATE  CEMENTS 


I 


Introduction 


The  so-called  silicate  cements  commonly  used  in  the  dental  pro- 
fession have  been  subjects  of  considerable  study  in  the  past , with 
particular  regard  being  paid  to  their  physiological  properties  as 
tooth  fillers.  These  cements  consist  of  finely  ground  powders,  set 
into  a cement  by  solutions  of  phosphoric  acid,  often  containg  modi- 
fiers of  aluminum  phosphate  or  related  compounds.  These  mixtures 
harden  quite  rapidly,  develop  considerable  strength,  and  do  not 
show  a great  amount  of  shrinkage.  The  main  constituents  are  Lime, 
Alumina,  and  Silica,  or  their  mineral  compounds,  and  various  other 
oxides  such  as  Bertflliuni, Zinc , and  Boron.  These  oxides  are  calcined 
or  fused  at  high  temperatures  in  the  course  of  their  preparation  as 
powders . 

The  present  work  is  based  on,  and  a continuation  of,  the  ex- 
periments carried  on  in  1916  as  a thesis  by  Joseph  William  Wright, 
The  results  of  this  former  work  makes  it  possible  to  materially  re- 
duce the  field  of  investigation,  and  to  specialize  in  the  determin- 
ation of  the  various  physical  properties  and  compositions  of  phos- 
phate cements. 


In  Wright’s  work  the  compositions  of  the  powders  used,  varied 
to  cover  nearly  all  of  the  ternary  system.  Lime,  Alumina,  and  Sili- 
ca. The  liquids  used  for  setting  vary  in  strength  of  Phosphoric 


II 


Scope  and  Results  of  Former  Work 


Acid  from 


include  also  some  solutions  con- 


T 


• 

. 

4 .4 

" 


4 ' - 


. 

. 


T 


. 

' 


' 

. 


r\ 

*C.m 


taining  modifiers.  The  powders  were  calcined  at  various  tempera- 
tures and  the  crushing  strength,  time  of  set,  and  heat  developed 
at  setting  were  determined  for  each  variation  of  heat  treatment, 
material  and  acid  concentration. 

The  results  show  that  mixtures  of  the  compositions  CaO.SiOg 
and  CaO.Al^O^  , when  calcined  at  a high  temperature .harden  readily 
with  phosphoric  acid  solutions.  The  calcium  aluminate  develops 
considerable  strength.  Calcined  mixtures  of  lime  and  clay  showed 
better  working  properties,  set  well  and  developed  excellent  strength 
Increase  of  acid  concentration  decreases  the  rate  of  setting,  gives 
less  heat  in  setting  and  lowers  the  porosity  of  the  hardened  ce- 
ment. The  addition  of  A12(P0^)2  to  the  solution  retards  setting. 

an 

The  presence  of  hygroscopic  water  in  the  powder  seems  to  have  im- 

A 

portant  effect  on  the  setting  properties.  As  commercial  cements, 
the  composition  C . A . s2  » and  CA^S^  mad«  from  clay  (N.  Carolina 
Kaolin),  and  Whiting,  and  mixed  with  liquids  containing  60 and 
75 1°  of  phosphoric  acid  were  found  to  give  the  most  satisfactory 
results . 

Ill 


Basis  of  Study 

These  mixtures  form  the  foundation  upon  which  this  study  is 
built.  Both  of  these  mixtures  lie  within  the  field,  on  the  tri- 
axial  diagram  of  Lime,  Alumina,  and  Silica,  which  is  bounded  by 
S,  AS  and  CA  2S.  If  these  mixtures  were  entirely  melted  and  al- 
lowed to  cool,  they  would  therefore  crystalize  out  into  the  three 
compositions  of  SiC>2  » AI2O3  , Si02  * and  CaO  .AI2O3  ,2Si02  > but 

if  they  are  not  cooled  in  equilibrium  or  have  not  all  gone  to  the 
liquid  phase,  there  may  be  other  compounds  present  on  cooling  which 


' •• 


v . 


..  ■ 


V 

*• 

■ 


. j - . 

•• 

- -■  ’ 


V- 


• ..  i 

♦ 


I*.;  ' 


; . 


■ i 1 


■ ! 


i. 


. 


■ 


v,  ■ 


. . 

J 


■ '•  . 


: 

* 


' - * > 


■ 


C ' ' 

. 


-4~ 

would  fall  in  some  of  the  adjoining  fields.  The  limits  set  for  si- 
licate cements  by  Dr*s.  W.  and  D.  Asch1  are  : 

CaO  6 to  12  percent 

A120^  “to  50  percent 

SiC>2  40  to  44  percent 

These  limits  also  fall  almost  entirely  within  this  area  on  the  tri- 
axial  as  shown  by  Figure  1«  This  diagram  of  the  triaxial  field 
shows  the  areas  of  crystalization  near  the  compositions  studied. 

The  limits  as  shown  above  are  plotted,  and  it  can  be  seen  that  a 
small  area  (shown  shaded)  is  within  all  limits  found  in  commercial 
cements.  This  area  shall  hereafter  be  referred  to  as  the  "most 
probable  area*. 

In  Figure  1,  the  compositions  studied  by  Wright  are  designated 
by  email  red  circles,  the  compositions  showing  particular  promise 
are  crossed.  The  boundaries  of  the  areas  of  crystalization  are 
shown,  as  well  as  the  area  in  which  are  found  the  commercial  Port- 
land cements.  All  compounds  are  marked,  and  the  compositions 
studied  in  the  present  investigation  are  designated  by  small  black 
circles . 


to 


IV 

Preliminary  Study 
A,  Objects. 

Preliminary  studying  the  specific  properties  of  any  cement  to 

A 

a large  degree  it  was  considered  advisable  to  determine  the  most 
satisfactory? 

(l)  Body  Composition. 

^ Silicates  in  Chemistry  and  Commerce. 


-5' 


(2)  Clay  material. 

(3)  Temperature  of  calcination. 

(4)  Percentage  of  Phosphoric  acid  for  short  time  tests. 

B.  Selection  for  Study. 


(l)  In  order 

to  study  the 

effect  of 

composition 

within 

a fairly 

small  range,  four 

bodies  of  the 

following  compositions  were 

select- 

ed: 

Body  No. 

1 

2 

3 

4 

CaO 

20$ 

6$ 

6$ 

10$ 

A12°3 

42$ 

56$ 

42$ 

4S$ 

Si02 

3S$ 

3S$ 

52$ 

42$ 

As  is  shown 

in  the  diagram 

, No.  1 is 

located  in 

the  field 

CaO .AlgO^ .2Si0g  - 

2Ca0 .AlgO^ .SiOg  - AlgO^ 

, and  contains  the 

most 

lime}  No.  2 is  located  on  the  boundary  line  between  the  fields 


SiO?,  CaO .AlgOj .2SiC2  - Al^O^.SiOg  and  CaO.  AlgO-^ ,2Si0g-  Al^O^. 

SiOg  - AlgO^,  and  contains  the  greatest  amount  of  A120^;  No.  3 con- 
tains the  most  SiOg  and  is  located  in  the  field  SiOg  - AlgO-^.SiOg- 
Cao.  Alg0^.2Si0g;  and  No,  4 is  located  in  the  center  of  the  "most 
probable  area".  These  bodies  are  made  from  the  following  mater- 
ials! 

Whiting  CaCO-? 

J 

Clay  (as  far  as  possible) 

Aluminum  Hydroxide  Alg(OH)^ 

Flint  Si Op 

(2)  In  the  former  study  only  one  clay  substance  was  used.  As 
clays  vary  considerable  in  their  physical  properties,  it  was  thought 
advisable  to  test  the  effect  of  a variation  in  the  clay  ingredients 


-6- 


by  making  each  body  with  the  following  clays? 

A.  North  Carolina  Kaolin 

B.  Florida  Kaolin 

C.  English  Kaolin 

(3)  As  former  mixtures  had  been  calcined  only  at  high  tempera- 
tures,  it  was  decided  to  test  the  range  of  the  temperature  of  cal- 
cine by  firing  each  body  to  the  following  temperatures? 

(a)  1200  Deg,  C 

(b)  1000  Deg,  C 

(c)  S00 

(d)  600 

(4)  The  two  strengths  of  acid  concentration  found  to  be  most 
desirable  for  developing  strength,  and  as  possibilities  for  further 
study  are? 

Per  Cent,  H-,P0^  Specific  Gravity 

by  Wt, 

75  1.57 

60  1.4l 

C.  Preparation  of  Powders. 

(1)  Calculating  and  Weighing? 

The  batches  were  calculated  and  weighed  according  to  the 
ceramic  formulas  of  pure  substances.  The  deviations  of  actual 
analyses  on  the  clays  used  from  theoretical  composition  is  not 
sufficiently  great  to  warrant  their  use, 

(2)  Molding  and  Drying  of  Raw  Materials? 

Each  batch  wae  mixed  thoroughly  on  oilcloth,  with  suffi- 
cient distilled  water  added  to  make  plastic,  and  molded  in 
brass  molds  1"  x ln  x 6",  The  resulting  bars  were  dried  at 


( \ 
> 


( ■ 


-7- 


room  conditions  for  a day  and  then  were  placed  in  a drier  at 
60  Deg.  C.,  and  kept  there  until  placed  in  the  kiln  for  cal- 
cination. 

(3)  Calcining: 

The  bars  were  calcined  in  covered  saggars  in  an  open  gas 
fired  kiln.  The  temperature  was  measured  by  a platinum  - 
platinum  rhodium  thermocouple  and  galvanometer.  The  maximum 
temperature  was  maintained  for  half  an  hour  and  then  the 
burners  were  turned  off. 

(4)  Grinding  and  Screening? 

After  removing  from  the  kiln  the  pieces  were  kept  in  a 
drier  at  60  Deg.  C.  until  ready  to  be  ground.  In  grinding 
the  material  was  crushed  progressively  in  (l)  jaw  crushers, 

(2)  roll  crushers  and  (3)  small  porcelain  ball  mills  (dry). 

The  grinding  in  the  mills  was  continued  only  until  about  90 $ 
or  over  of  the  material  could  pass  a 150  mesh  seive.  After 
removal  from  the  ball  mills,  the  powders  were  screened  in  a 
Ro-Tap  machine  to  pass  150  mesh.  The  residue  on  the  screen 
was  returned  to  a ball  mill  and  ground  to  pass  150  mesh. 

(5)  Mixing  and  Molding: 

Because  of  the  large  quantities  of  materials  to  be  mixed, 
the  practice  of  the  dental  profession  could  not  be  strictly 
followed.  Instead,  the  powdered  materials  were  mixed  frith 
the  phosphoric  acid  solution  in  a porcelain  mortar  with  a 
porcelain  pestle.  The  entire  portion  of  powder  (about  60  grams’ 
was  placed  in  the  mortar  and  then  covered  with  the  desired 
amount  of  acid.  By  stirring  with  the  pestle,  more  acid  being 
added  if  needed,  the  mixture  was  brought  to  the  consistency 


V 


* 


f N 


— 

. 

. 

J 

• 

♦ 

f ' 

* ' ) 
- 

. . . . ■ 

. 


* 


' 


■l''  : 

' , ■■■, 


. 

. . 

. 


-g- 

of  a stiff  paste o This  method  did  not  lead  to  a great  amount 
of  symmetry  between  the  separate  mixes.  The  molding  was  done 
by  forcing  the  plastic  material  into  wooden  molds,  forming 
cylinders  3/^*  in  diameter  and  1 1/4"  high.  Each  mold  made 

five  cylinders,  measured  S"  x 1 1/4"  x 1 5/8*  and  was  care- 

f 

fully  coated  with  paraiine  before  each  filling.  The  molds 

A 

were  split  thru  the  center,  forming  a perfect  half  on  each 
side,  in  order  to  aid  in  removing  the  cylinders.  During  the 
time  of  molding  and  until  the  next  mold  was  to  be  filled,  the 
molds  were  held  together  by  two  small  clamps  over  the  ends  and 
were  placed  on  glass  plates  to  form  perfect  ends  to  the  cylin- 
ders. The  material  was  forced  into  the  molds  with  a porcelain 
spatula,  covered  with  another  glass  plate,  and  subjected  to  a 
load  of  10  lbs.  until  the  next  mold  was  ready  (about  10  min.) 

(6)  Setting! 

The  test  pieces  were  allowed  to  set  in  the  molds  under 
room  conditions  for  the  first  24  hours.  After  this  period 
they  were  entirely  exposed  to  the  open  air  for  the  remainder 
of  the  seven  days  which  was  allowed  for  setting  before  crush- 
ing strength  tests  were  made. 

(7)  Crushing  Strength! 

The  crushing  strength  was  determined  in  a 10000  lb.  Tinius 
Olsen  testing  machine  located  in  the  Fatigue  of  Metals  Labora- 
tory at  the  University  of  Illinois.  The  cylinders  were  sup- 
ported on  both  ends  by  small  bearing  plates  (l/2"  steel  balls) 
and  padded  with  two  layers  of  blotting  paper.  Five  test  pieces 
were  used  for  each  mix.  All  were  not  perfect,  however,  and 
many  were  discarded. 


•f 


* 


’ 


. . . 

: < 

f ' 


* 


. 

' i ’■  r . . 


■ .. 

f . ' 


...  • _ . 1 . rr.iv  •. . 

..  . 


. 


. 

) . 


. 


. 


-9“ 

Do  Results o 

(1)  Working  properties: 

When  in  a plastic  condition,  the  Florida  Kaolin  gives 
the  best  working  properties,  the  English  Kaolin  is  next  in 
order,  followed  by  the  N.  Carolina  Kaolin,  The  mixture  of 
Feldspar  barely  held  together, 

(2)  Calcination: 

The  bars  of  Feldspar  mixture  were  the  only  examples  of 
deformation  of  any  kind.  These  bars  showed  some  signs  of 
fusion  over  surface. 

Actual  temperature  attained: 

(a)  1210  Degrees  C. 

(b)  1050 

(c)  S00 

(d)  600 

(3)  Grinding  and  Screening: 

Observations  of  the  length  of  time  required  to  grind  the 
powders  in  the  ball  mills,  and  to  screen  them  showed  that  the 
mixtures  made  from  Florida  Kaolin  calcined  into  the  hardest 
mass  at  each  temperature,  the  English  Kaolin  next,  and  the 
N.  Carolina  Kaolin  broke  up  very  easily  into  seemingly  large 
grains , 

The  average  number  of  revolutions  in  ball  mills  required 
to  grind  the  Florida  Kaolin  mixtures  was  225,000  while  the 
number  of  revolutions  for  N.  Carolina  Kaolin  mixtures  was 
125,000,  The  Florida  Kaolin  gave  all  evidences  of  being  the 
finest  grained  material  and  the  most  easily  vitrified. 


( \ 
( \ 


/ 


. 


. 


-10 


(4-)  Setting: 

The  amount  of  setting  shrinkage  seem3  to  be  slightly 
greater  for  powders  made  from  Florida  Kaolin.  This  shrinkage 
was  estimated  from  the  ease  with  which  the  cylinders  were  re- 
moved from  the  molds. 


(5)  Crushing  Strength! 

(a)  Powders  calcined  at  1210  Degrees  C. 


Powder 

Acid  Con- 

Average 

Characteristics 

No, 

centration 

Crushing  Strength 

75 

1A 

60 

Set  immediately 

75 

IB 

60 

H » 

75 

1C 

60 

H It 

75 

2A 

60 

1100 

(1  test) 

75 

2B 

60 

75 

2C 

60 

— 

3A 

75 

— 

60 

— 

75 

1130 

(3  tests) 

3B 

60 

1215 

(4  tests) 

3C 

75 

— 

60 

7&0 

(l  test) 

4A 

75 

— 

60 

I ' 


' - 


' 


■ 


Powder 

Acid  Con- 

-11- 

Average 

Characteristics 

No. 

centrat ion 

Crushing  Strength 

4B 

75 

665 

(4  tests) 

60 

1750 

(2  tests) 

75 

600 

kc 

60 

75 

600 

Set  immediately 

Spar 

60 

(b)  Powders 

calcined  at  1050  Degrees 

C, 

Powder 

Acid  Con- 

Average 

Characteristics 

No, 

centration 

Crushing  Strength 

1A 

75 

60 

Set  immediately 

IB 

1C 

75 

60 

75 

60 

75 

It  « 

« « 

Soft 

2A 

6o 

— 

Stiff 

75 

— 

Soft 

2B 

60 

1200 

Stiff  (2  tests) 

75 

Soft 

2C 

60 

500 

Stiff 

75 

Set  too  quickly 

3A 

60 

soo 

(l  test) 

75 

3B 

6o 

75 

3C 

6o 

-12- 


Powder 

Acid  Con- 

Average 

Characteristics 

No. 

centration 

Crushing  Strength 

4A 

75 

Set  too  quickly 

60 

4b 

75 

* w it 

60 

4C 

75 

* « H 

60 

75 

Spar 

60 

Set  immediately 

(c)  Powders  calcined  at  800  and  600  Degrees  C. 

All  of  these  powders  set  too  quickly  for  placing  in 
molds  and  so  gave  no  information  as  to  their  character- 
istics,. 

E0  Conclusions* 

(a)  A survey  of  the  results  obtained  by  variations  in  the 
body  compositions  indicates? 

(1)  The  speed  with  which  the  initial  reactions  of  setting 
take  place  varies  directly  with  the  percentage  of  CaO  in  the 
mixture.  This  is  shown  by  the  fact  that  No.  1 composition 
shows  the  first  signs  of  such  initial  set  and  that  No.  4 con- 
taining the  next  largest  percentage  of  CaO  is  the  next  in 
order „ 

(2)  The  addition  of  1^3  part  feldspar  as  a fluxing  mater- 
ial greatly  increases  the  speed  of  initial  set. 

(3)  The  compositions  located  entirely  in  the  field  SiOg  “ 
AlgO-^.SiOg  - Cao.  Al^O-^ . SiQ2  are  the  most  satisfactory.  The 
lower  percentage  of  lime  in  No.  3 makes  it  a slower  setting 


* ( ' 


_ 

■ 

► 

* 

% 

( 

' ' 

. 

. 

. 

. 

< I 

. 


-13- 

mixture  « 

(4)  The  highest  crushing  strength  is  found  in  composition 
No.  k-9  located  in  the  center  of  the  "most  probable  area"* 
Selection  for  further  study;  Composition  No. 

(b)  Results  of  the  variations  of  clay  material  indicate; 

(1)  A more  satisfactory  white  color  is  obtained  from  Flori- 
da Kaolin  and  English  Kaolin  than  from  North  Carolina  Kaolin. 
This  difference  becomes  more  noticeable  as  the  temperature  of 
calcination  is  decreased. 

(2)  The  best  working  properties  both  in  mixing  the  materials 
before  calcination  and  for  mixing  with  the  acid  solutions,  as 
well  as  the  highest  crushing  strength  are  found  with  the  mix- 
tures made  with  Florida  Kaolin, 

Selection  for  further  study;  Florida  Kaolin. 

(c)  The  results  of  variations  in  the  temperature  of  calcina- 
tion indicate; 

(1)  The  speed  of  the  reaction  of  initial  set  increases  with 
a decrease  in  the  temperature  of  calcination. 

(2)  The  crushing  strengths  obtainable  are  higher  with  a 
higher  temperature  of  calcination. 

Selection  for  further  study;  1250  Degrees  C. 

(d)  Variations  in  the  strength  of  acid  solutions  indicate; 

(l)  The  concentration  of  6o$>  phosphoric  acid  gives  the 

highest  results  in  crushing  strength  for  a period  of  setting 
of  one  week. 

Selection  for  further  study;  A 60 $ solution  of  phosphoric  acid 
in  distilled  water. 


. 


-14- 

V 

Final  Study 
A.  Object® 

In  a final  study  it  was  desired  to  determine  the  effect  of: 

(1)  Slight  variations  in  the  proportion  of  dry  material  to 

acid. 

(2)  Moisture  and  vapor  pressures  during  period  of  initial 
set  as  determined  by  crushing  strength. 

(3)  Moisture  and  vapor  pressure  after  initial  set  as  deter- 
mined by  crushing  strength. 

It  was  also  desired  to  obtain  by  the  use  of  somewhat  larger 
cylinders,  more  reliable  data  upon  the  crushing  strnegth  obtain- 
able with  this  type  of  cement. 


B.  Preparation  of  Powders 
(l)  Composition  and  Materials: 

(a)  A body  of  the  following  composition  was  prepared: 

CaO  10fo 

A12°3 
SiOg 

(b)  Materials: 

Material 


Whiting 
Florida  Kaolin 


Approximate 

formula 

CaCO^ 

A120^.  2Si02.6H20 


Aluminum  Hydroxide  Alp(OH)^ 


Batch 

Wt, 

537  gram 
2709 
564 


Total  3S10  gram 


(c)  Acid  Solution: 

The  acid  solution  oontained  60%  by  weight  of  H^PO^, 


. 


« 

* 

% 

( 


-15- 


and  a small  quantity  of  Al^PO^Jg  or£*®r  to  retard  the 
rate  of  setting.  The  specific  gravity  of  the  liquid  be- 
fore the  addition  of  the  Al^  (P0^)2  was  1.4-1. 

(2)  Mixing  and  Calcinings 

The  finely  powdered  materials  from  stock  were  mixed  on 
an  oilcloth,  passed  thru  a 20  mesh  seive,  and  mixed  again. 

This  assured  a thorough  mixing  and  a satisfactory  fineness 
of  material.  The  powder  was  then  placed  in  new  clean  saggars, 
wadded  tightly  and  fired  in  a coal  fired  test  kiln.  A plati- 
num-platinum rhodium  pyrometer  registered  1150  Degrees  C.  on 
a galvanometer . Orton  pyrometric  cones  placed  in  the  kiln 
showed  that  a heat  treatment  of  Cone  5 was  attained. 

(3)  Grinding  and  Screening? 

The  calcined  material  was  ground  in  small  porcelain  ball 
mills  as  before,  and  screened  through  a 150  mesh  seive  in 
Ro-Tap  machine.  The  residues  on  the  screens  were  small  and 
gave  the  same  results  with  acid  tests  as  were  found  with  the 
screened  materials. 

(4-)  Mixing; 

A definite  proportion  of  powder  to  acid  was  attained  by 
weighing  out  exactly  75  grams  of  the  powder  for  each  batch. 

The  acid  solution  was  measured  to  l/2  cubic  centimeter  in  a 
50  c.c.  graduate.  In  order  to  make  the  mixing  more  uniform 
throughout  the  short  period  of  stirring,  a small  quantity  of 
the  powder  at  a time  was  added  to  the  mortar  and  partly 
covered  with  acid  solution.  In  order  to  keep  the  initial  set 
as  low  as  possible,  the  acid  solution  was  kept  in  a bath  of 
cold  water.  Two  consistencies  were  used  for  each  test.  The 


. 


■ 


- 


. 


. 

* 

\ 

. 

' 

. 

. 


. 


. 


-16- 

first  contained  37  cc.  of  acid  solution,  and  had  the  consis- 
tency of  plastic  putty.  The  other  contained  40  c.c.  of  acid 
solution,  and  worked  into  a creamy  paste,  which  flowed  quite 
readily  from  a porcelain  spatula.  In  commercial  practice 
it  would  be  very  easy  to  remain  within  even  smaller  limits  by 
an  observation  of  the  consistency  of  the  paste. 

(5)  Molding! 

The  molding  was  done  in  the  wooden  molds,  as  in  the 
preliminary  work.  The  interiors  were  waxed  as  before,  but 
the  surfaces  of  the  glass  plates  used  to  form  the  ends,  were 
covered  with  a thin  film  of  oil  to  avoid  sticking  to  the 
plates.  After  the  pasty  material  had  been  forced  into  molds 
with  porcelain  spatula,  a pressure  of  approximately  5 lbs. 
was  applied  by  a small  wooden  piston,  forcing  the  material 
more  compactly  into  the  mold.  The  mold  was  again  filled 
to  the  top  and  compressed  by  the  spatula.  During  the  period 
of  preparation  of  another  mold,  a force  of  10  lbs.  was  applied 
to  the  upper  glass  plate.  Ten  test  pieces  were  prepared  for 
each  test,  five  being  of  37  c.c.  mix  and  five  of  4-0  c.c.  mix. 

(6)  Setting: 

The  period  of  initial  set  is  assumed  as  the  first  24- 
hours.  2 Seven  variations  in  the  conditions  of  setting  were 
made  as  follows: 

1.  The  first  24-  hours  in  the  mold  under  atmospheric 
conditions,  followed  by  6 days  entirely  exposed  to  atmos- 
pheric conditions. 

p 

Morgenstern,  Osterr .-Ungas . Vierteljahrschr . f. 
Zahnheilk  1905  p.535 


- 


- 


r . 

! 

* 


. 


, 


t-  i 


. 


. 

. 


-17- 


2,  The  first  24-  hours  in  the  mold  under  atmospheric 
conditions,  followed  by  the  final  period  of  set  completely 
exposed  to  an  atmosphere  of  high  vapor  pressure,  and 
100%  relative  humidity, 

3 o The  first  24-  hours  in  the  mold  under  atmospheric 
conditions,  followed  by  6 days  of  final  set  completely 
immersed  in  distilled  water, 

4-,  The  first  24-  hours  in  the  mold  under  atmospheric 
conditions,  followed  by  a final  setting  period  of  6 day% 
entirely  exposed  to  an  atmosphere  of  low  vapor  pressure, 
5,  The  first  24-  hours  in  the  mold  under  conditions 
of  high  vapor  pressure,  followed  by  a period  of  6 days 
completely  exposed  to  atmospheric  conditions, 

6*  The  first  24-  hours  in  the  mold  under  conditions 
of  low  vapor  pressure,  followed  by  a period  of  6 days, 
compdetely  exposed  to  atmospheric  conditions, 

7.  The  first  24-  hours  in  the  mold  and  immersed  in 
distilled  water,  followed  by  a period  of  6 days  complete- 
ly exposed  to  atmospheric  conditions, 

(7)  Crushing  Test: 

The  crushing  strength  was  determined  in  the  same  manner 
as  in  the  preliminary  work.  The  only  difference  being  that 
for  the  final  work,  the  cylinders  for  each  test  were  arranged 
in  the  order  of  their  visible  perfection  before  crushing. 


■ 


i 

• 

« 

• 

- 

» 

V 

« 

1 

t 

• 

( ' 

-IS- 

C.  Results 

(a) 

General  Atmospheric  Data: 

Day  Wet  Bulb 

Dry  Bulb 

Relative 

Vapor  Pressure 

Humidity 

(Carrier) 

1 

60°  C 

72i°  C 

50$ 

0.400 

in  Hg. 

2 

6l 

70 

60 

0,425 

3 

620c 

72 

56 

0.420 

4 

64 

71 2 

6S 

0 .480 

5 

63 

72 

60 

0,450 

6 

63 

72 

60 

0,450 

7 

63 

73 

5$ 

0.450 

g 

66 

73 

66 

0.520 

9 

69 

7&i 

70 

0.5S0 

10 

68 

74 

75 

0.575 

11 

69 

75 

79 

0.610 

(b) 

Conditions  for  each 

test: 

(1) 

Atmosphere  - Atmosphere 

Temperature  of 

Initial  Set 

22*5° 

c 

Vapor  Pressure 

of  Initial 

Set 

0.400 

in  Hg. 

Ave.  Temp.  Final  Set 

22.6 

Ave.  Vapor  Pressure  Final 

Set 

0.45 

(2) 

Atmospheric  - High  Vapor: 

Temperature  of 

Initial  Set 

22,50 

c 

Vapor  Pressure 

of  Initial 

Set 

0.400 

in  Hg. 

Temperature  of 

Final  Set 

22,6 

Ave.  Vapor  Pressure  Final 

Set 

0.675 

(3) 

Atmosphere  - Immersed: 

Temp,  of  Initial  Set 

22.22 

Vapor  Pressure 

Initial  Set 

0.420 

-19' 


Ave,  Temp.  Water  Final  Set  21.0 

(4)  Atmosphere  - Low  Vapor  Pressure 

Temperature  of  Initial  Set  22.22 

Vapor  Pressure  of  Initial  Set 

Ave.  Temperature  of  Final  Set  22,6 

Ave.  Vapor  Pressure  of  Final  Set 
(Vapor  pressure  over  95 i°  HgSO^. 
at  22°  C as  determined  by  inter- 
polation of  values  found  in 
Physical  Chemical  Tables  * 

Landolt  & Bbrnsteln.) 

(5)  High  Vapor  Pressure  - Atmospheric 


0.4-20 


0.0Q09S5 


Temperature  of  Initial  Set 

22.22 

Vapor  Pressure  of  Initial  Set 

0.630 

Ave.  Temperature  of  Final  Set 

23.5 

Ave.  Vapor  Pressure  of  Final  Set 

0.531 

(6)  Low  Vapor  Pressure  - Atmospheric 

Temperature  of  Initial  Set  22.22 

Vapor  Pressure  of  Initial  Set  0.Q009&5 

Ave.  Temperature  of  Final  Set  23.5 

(7)  Immersed  - Atmosphere 

Temperature  of  Water  21. 5 

Ave.  Temperature  of  Final  Set  23 »5 

Ave,  Vapor  Pressure  of  Final  Set  0.533- 


■ 


l \ 


-20- 


(c)  Compression 

Test: 

Setting 

Acid 

Actual  Load 

Average 

Conditions 

c .c . 

in  lbs. 

(1) 

Atm.  - Atm. 

40 

2280 ,2500 ,2500 ,2700 ,2500 

2496 

37 

2720 ,3000 ,1920 ,1840 ,Bend 

2537 

(2) 

Atm.  - High  Vap, 

40 

2200 ,2500,2800,2200,2900 

2520 

37 

2860 ,Bend ,2800 ,2700 ,1800 

2727 

(3) 

Atm.  - Immersed 

40 

2300 ,1800 ,1750,1700 ,2100 

1930 

37 

2500,1800 

2150 

(4) 

Atm.  - Low  Vap. 

40 

3400,3100,3260,3300 

3265 

37 

2000,2000,(1900,1800  short] 

) 1925 

(5)  High  Vap.  - Atm. 

40 

2300 ,2200  ,2000  ,2500  ,2800 

2360 

37 

2500,2000,1500 

2000 

(6) 

Low  Vap.  - Atm. 

40 

3500,3300,3250 

3350 

37 

3200,3200,2500,2900 

2950 

(7) 

Immersed  - Atm. 

40 

1400,1700,1400,1000 

1375 

37 

1100,  700,1700  (short) 

1166 

-21- 


(d)  Average  strength  according  to  proportion  of  acid  to 
Powder; 

Average  strength  of  mixtures  containing  40  c.c,  24/1  lbs 
" " « « « 37  c.c.  2216 

(e)  Highest  Average  Crushing  Strength  expressed  in  lbs  / sq.in. 
is  6130  #/  sq.  in* 

Do  Conclusions,, 

(a)  Variation  in  the  proportion  of  dry  material  to  acid  solu- 
tion indicate  that; 

(1)  Very  small  changes  in  the  proportion  of  powder  to 
acid  solution  give  marked  differences  in  the  plasticity  of  the 
mixture . 

(2)  The  results  obtained  are  not  consistent  enough  to 
warrant  any  conclusions  as  to  the  effect  upon  the  compressive 
strength • 

(b)  Variations  in  the  moisture  and  vapor  pressure  treatment 
during  the  period  of  initial  set  indicate  that; 

(1)  The  highest  crushing  strength  is  developed  under  con- 
ditions with  the  lowest  vapor  pressure, 

(2)  The  setting  of  the  cement  under  water  does  not  pro- 
duce cements  of  sound  structure  or  of  high  crushing  strength. 
This  indicates  that  these  cements  are  not  hydraulic  in  their 
reactions,  . 

(c)  Variations  of  the  moisture  and  vapor  pressure  treatment 
during  the  period  of  final  set  indicate  that; 

(l)  The  highest  crushing  strength  is  developed  under  con- 
ditions of  low  vapor  pressure. 


• * 


' > 


* 


* 


-22- 

(2)  The  final  setting  under  water  gives  lower  values  in 
crushing  strength  than  are  found  with  the  same  cements  set 
under  moist  or  dry  conditions, 

(d)  The  study  with  variations  both  in  the  period  of  initial 
set  (24  hours)  and  in  final  set  (6  days)  indicate  that! 

(1)  The  period  of  initial  set  is  the  period  containing 
the  principle  chemical  change,  as  shown  by  variations  in 
values  under  these  conditions, 

(2)  The  chemical  changes  are  not  complete,  however,  in 
the  initial  period  but  give  all  evidence  of  undergoing  pro- 
gressive change  over  a period  of  days  or  months  after  being 
mixed, 

VI 

Summary . 

Compositions  of  Lime,  Alumina  and  Silica  producing  workable 
phosphate  silicate  cements  were  found  to  lie  in  the  field  of  crys- 
talization  S,  AS,  CA2S.  The  most  promising  cement  is  developed 
from  the  composition! 


CaO 

10fo 

Al^O-^ 

4S 

Si02 

42 

The  character  of  raw  materials  used  has  a very  marked  effect 
upon  properties  and  behavior  of  the  cement.  Florida  Kaolin  as  the 
clay  material  gives  the  highest  crushing  strength,  and  the  most 
desirable  working  properties,  as  well  as  good  color. 

The  speed  of  the  initia.l  setting  reaction  increases  with  in- 
crease in  percentage  of  CaO  in  the  composition. 

A high  temperature  of  calcination  is  the  most  satisfactory 


' 


. 


■ 

. 


-23“ 

for  the  preparation  of  the  powders,  and  indicates  that  fusion  of 
the  materials  may  be  desirable. 

The  proportion  of  powder  to  acid  solution  has  no  particular 
relation  to  the  physical  properties  of  the  hardened  cement. 

The  principal  chemical  change  takes  place  within  the  first 
24  hours  of  setting,  but  a progressive  chemical  action  continues 
for  some  days. 

The  cements  with  the  highest  crushing  strength  result  from 
setting,  both  during  the  initial  and  final  period,  under  conditions 
of  low  vapor  pressure.  This  is  in  agreement  with  statements  made 
by  Dr*s  W.  and  D.  Asch3. 

The  highest  crushing  strength  obtained  on  a 7 day  test  was 
slightly  over  6000  lbs.  / sq.  in.  This  was  on  a cylinder  made 
from  the  composition: 


CaO 

10$ 

A12°3 

48 

SiG2 

42 

The  clay  material  was  Florida  Kaolin,  and  the  conditions  of 
setting  were: 

Initial  set  under  low  vapor  pressure. 

Final  set  under  atmospheric  conditions. 


3 Silicates  in  Chemistry  and  Commerce.  Dr*s  W.  and  D.  Asch 

Hardening  of  Dental  Cements  p.218. 


